http://www.nature.com/nature/journal/v468/n7323/full/nature09579.html
This work done by James M. Tour's group will certainly be a huge impact in graphene production.
They show that the graphene can be grown by solid state materials like polymer, more incredibly, they said that they can even control the layer number of synthesized graphene by tuning the annealing condition, such as the flow rate of Ar and H2 gas during the growth process.
They accounted for this effect by introducing an idea that H2 is able to serve as reducing agent as well as a carrier gas to remove carbon released from PMMA. And the hydrogen flow rate is essential since the remain carbon sources determined the number of layer will grow.
In addtion to the PMMA-derived graphene, they also used fluorene and sucrose to demonstrate the possible way to grow monolayer graphene.
Moreover, they blended melamine and PMMA and make them into N-type graphene by introducing some nitrogen atoms in the framwork of carbon.
They really did an incredible job, it seems that anything contain carbon can be used to grow the graphene. That sounds pretty amazing, doesn't it?
Showing posts with label Paper Review. Show all posts
Showing posts with label Paper Review. Show all posts
Self-aligned nanowire gate graphene transistor !
The groups who formed GNR with the aid of nanowire now have enormous advance in top-gated graphene transistor.
Their paper was published in Nature in just two days before.
They used a Co2Si–Al2O3 core–shell nanowire as a top gate electrode which is able to apply an electric field across the thin layer of Al2O3 that serve as a gate dielectric. Apparently, the gating effect would be far more large than that of back-gated configuration, since the dielectric layer is extremely thin and possess higher dielectric constant than SiO2. To fulfill the requirements of microwave measurement, they replaced the degenerate silicon substrate with highly resistive ones that could effectively reduce the dielectric loss at microwave frequency. And they found that the cutoff frequency could be up to 300GHz, which increases the usability of graphene transistor at high frequency.
Two groups drilled nano scale pores for DNA passing through !!!
As mentioned in my previous article, two groups, from Upenn and Netherlands, have already put this idea into practice. They really drill a nanopore on the sheets of graphene!!
both of them have been published in Nano Letters,
This one is from a famous group in the field of biosensor lead by Cees Dekker
And this one is from Upenn, Datta's previous lab lead by A.T. Charlie Johnson, they are the pioneer that found a way to sense the gas odor by DNA-decorated carbon nanotube
They realized this idea by recording the blocked current change while the DNA were passing through these holes, and they found the current change profile corresponding to the two states of DNA; the signals could be used to distinguish the DNA either folded or unfolded as it pass through a pore. These DNAs were driven by a potential difference across the graphene membrane, which allows the measurement of the passing of DNA.
In my view, it is not dfficult to imagine that the ion distribution outside the giant biomolecules such as DNA and protein would somehow change to adapt these intruders and tend to maintain charge neutrality in the solution. As these molecules approach the surface of graphene, the graphene nanopore device can detect this considerable or even quantitative change in ionic condition in terms of the pulses that decrease in current. I believe that it is just the first step for DNA sequencing. The difficulty of this final goal is possible to be limited to rate of detection, since the transient signal is hard to be used in distinguishing the single-base pair differences.
CNT-FET controlled by an ion pump gate
The above is a very impressive work from Lawrence Livermore National Laboratory!
They utilized a lipid bilayer with ion pumps to cover the CNT-FET.
The ion pump as mentioned above, is made of ATPase which is powered by ATP hydrolysis; the ATPase is able to control the ion gradients across the membrane by metabolizing ATP.
They used a single semiconducting CNT to conduct this experiment and proved that the ATP can indeed act like a trigger to open the gate of ion pump, which is evidenced by the drain current change.
Moreover, they conjugated the head group of lipid with FITC which monitored the pH variation in the aqueous layer between CNT and lipid membrane. Finally, they explained that the drain current saturation is due to a small leak passage in the membrane or ion pump.
I think it is interesting to put a lipid on the top of CNT device, what if we put it on the graphene device?
Or maybe graphene itself can serve as a membrane or even we can even drill a hole on it to allow small biomolecules like DNA or RNA to pass through these holes, and we can monitor the ionic concentration change nearby the holes by recording the current change or something. It is not difficult to imagine that someone would think of this kind of idea, since in recent publication, the nanopore-related topics is also a very hot topic as graphene, both of them had appeared in Nano Letters or ACS Nano for many times.
Can we exfoliate graphene with the aid of solution?
The most common preparation of graphene is to exfoliate the graphite with scotch tape.
On the other hand, the researchers try to seek an alternative way to exfoliate the graphite stacks, that is, using various kinds of solvent to intercalate the graphite and exfoliate the stacks.
The most representational work is
Since the experiments in this paper seems to be relatively simple. I made a test immediately.
The solvent I chose is NMP (N-Methyl-2-pyrrolidone) which is the best solvent they concluded.
The mechanism is easily comprehended by the solvent-graphene interaction, but the main problem is that NMP is hard to evaporate in ambient condition. It can only be removed in vacuum with heat assistance.
After drying the solvent, the graphene flakes is so small to the extent that are difficult to process.
Meanwhile, something came to my mind, can we exfoliate the graphene sheets by similar technique used for dispersing CNT bundle?
So I test this idea with a surfactant called NaDDBS (sodium dodecylbenzenesulfonate) which were used in our previous study of CNT-FET biosensor. The results is better, I was so happy with that !
Immediately, I searched the literature to see whether it has been published or not....
And then.......I found this one.....
I was so depressed about it..............
It was too late, they already published their work in Feb, 2009.
The early bird catches the worm.......
Reducing GO with Flash light !??
Although the use of camera lash has been reported in CNT, Si nanowire and conducting polymer. This work still gave me a big shock.
http://pubs.acs.org/doi/abs/10.1021/ja902348k
Researchers from Northwestern University (the alma mater of my master adviser) had invented a new way to reduce graphite oxide. They used the commercial camera's flash light to irradiate the GOs and make them back to graphite and accounted for this effect by using photothermal heating mechanism. They found that the flash method is effective enough to compare with themal annealed samples. The basic principle is about the water evaporation from the GO, and the enough photo energy to trigger the deoxygenating process.
Taking advantage of flash light, they even make a photomask to define the device region. This is a very useful method for GO approach, and they demonstrated again that the camera flash is able to be a tool for reduction proecess.
I just wondering why the flash light irradiation in ambient condition could be a reducing agent for GO while being a oxide agent in other cases. @_@
http://pubs.acs.org/doi/abs/10.1021/ja902348k
Researchers from Northwestern University (the alma mater of my master adviser) had invented a new way to reduce graphite oxide. They used the commercial camera's flash light to irradiate the GOs and make them back to graphite and accounted for this effect by using photothermal heating mechanism. They found that the flash method is effective enough to compare with themal annealed samples. The basic principle is about the water evaporation from the GO, and the enough photo energy to trigger the deoxygenating process.
Taking advantage of flash light, they even make a photomask to define the device region. This is a very useful method for GO approach, and they demonstrated again that the camera flash is able to be a tool for reduction proecess.
I just wondering why the flash light irradiation in ambient condition could be a reducing agent for GO while being a oxide agent in other cases. @_@
Over 1 square centimeter graphene debut!!
No doubt this accomplishment is definitely an enormous progress for graphene research.
A famous group from UT Austin, lead by Rodney S. Ruoff, a leader who first carved up graphite into graphene in 1998, he also wrote a review article in Nature Nanotechonlogy in just few months earlier.
They found if the growth substrate for CVD graphene is replaced by a copper foil, the growth of graphene would be self-limited, which means it is hard to build the second layer on the top of the first layer graphene. With the help of the poor carbon solubility in copper during the synthesis process, the graphene is formed continuously across a vast area of substrate. Eventually, they concluded that the precipitation process of carbon on the surface of copper is suppressed at the high temperature, which enabled a large continuous graphene to be obtained.
The realization of getting a wafer scale and atomically thin graphene is a great progress, however, the absence of band gap in SLG has strongly limited the potential application in electronic industry. Nowadays, a vigorous trend is to open a band gap in graphene electronic device without degrading the transport properties. As far as I know, there are many groups are eagerly working on band gap engineering of graphene, one of these possibility is bilayer graphene, which has been shown to be able to get a band gap under the dual gate configuration. I believe that one day the dream of wafer scale CVD bilayer graphene will be realized. Unfortunately, in spite of my previous work is related to build a CVD system, I don't have chance and enough time to work on it...
UCLA researchers found the way to form GNR by Si-NW etching mask!!
I have to say this is really a brilliant idea to form a GNR by simply applying the nanowire as a mask.
Two groups from UCLA, lead by Yu Huang and Xiangfeng Duan, published this work in Nano Letters
I think it is very suitable for us to produce GNR in this way, since we have plenty of Si nanowires. In order to test it, I try to disperse Si nanowires by suspending them in an enthanolic solution. I found that it is hard to control the distribution and orientation of nanowires. Even though the nanowire has been deposit on the top of graphene, it is no guarantee that the nanowire would firmly contact the graphene to the extent that is able to protect the underlying graphene, which is hard to verify as well.
I think I would try to use some physical ways to deposit the nanowire if I have time to test it.